Discharge lamp circuit



Dec. 2, 1952 B. A. SAWYER ET AL 2,620,459

DISCHARGE LAMP CIRCUIT Filed Oct. 50, 1945 Brute A. jawyer LaurenceBurns INVENTORS ATTO RN EY Patented Dec. 2, 1952 UNITED STATES PATENTOFFICE DISCHARGE LAMP CIRCUIT of Massachusetts Application October 30,1945, Serial No. 625,586

1 Claim.

This invention relates to apparatus and circuits for operating electricdischarge lamps, particularly those having a thermionic cathode.

Such lamps have previously been operated with relays to allow preheatingof the filament, or directly from high voltage transformers without anypreheating of the filament. The first method produced an undesirable lagin starting after applying voltage to the circuit, and the secondproduced low efiiciency because of the increased starting voltage. Ourcircuit avoids both these difficulties, and allows prompt startingwithout much loss in efficiency.

An advantage of our invention is the provision of a high electrodeheating current for a very short time, and the reduction of this currentto a low value on starting of the lamp.

This is attained by using an additional winding on the usual choke coilof the ballast, connecting this winding in series with the electrodeheater, and proportioning and connecting this winding so that thevoltage induced in it by the normal operating current of the lampopposes the voltage of the source used for heating the electrode. I havereferred to the electrode heater, but of course in most discharge lamps,the electrode will consist of a coiled oxide coated wire which willserve at once as electrode and heater.

Other objects, features and advantages of the invention will be apparentfrom a consideration of the following specification, taken inconjunction with the accompanying drawings.

Fig. l is a plan view of a core suitable for the magnetic circuit usedin the invention; and

Fig. 2 is a schematic diagram of a circuit according to the invention.

In the latter figure, the lamps l and 2, which may be fluorescent lampsif desired, have the filamentary electrodes 3, 4, and 6, preferably ofcoiled tungsten wire coated with one or more of the alkaline earthoxides, one electrode being at each end of a lamp.

The filamentary electrodes 3, 4, 5 and 6 are connected, respectively tothe heating windings l, 8, 9 and I0, through the auxiliary windings ll,[2, l3, M, respectively. The heating windings are on a transformerconnected to the line, although any other suitable source of heatingvoltage may be used instead of such windings if desired. The auxiliarywindings H, l2, I3, [4 may be on the same core as the usual choke coilor inductance forming all or part of the lamp ballast.

The primary winding I 5 is connected to the line and the secondarywinding [6 is connected at one end to the choke coils I1, [8 leading tothe lamps l, 2, and at the other end to one end of the primary IS in theusual auto-transformer manner, the other side of the power supply to thelamp being the other end of the primary 15, which end is connected tothe electrodes 4 and 6 as the common return terminal.

The choke coil I1 is connected between one end of the autotransformersecondary l6 and the electrode 3, while the choke coil [8 is connectedto the electrode 5 in the same manner, except that the condenser 19 isinterposed in series between the choke coil [9 and the lamp 2 in theusual manner. The condenser may be of such a size that it places the twolamps suiiiciently out of phase to correct the power factor and reducethe stroboscopic effect from the pair of lamps. The .bleeder resistance20 may be used across the condenser.

When the power is first applied to the circuit, the voltage from theheater windings i, 8, 9, it! will produce a heating current in thefilaments 3, l, 5, 6. At this time there is no current through the lampitself, that is across the discharge space between the electrodes 5 and6, and 3 and 4, and hence no current through the choke coil ll. There isthus no counter voltage induced in the coils ll, 12, i3 and I4, andhence the flow of current in the filaments is not greatly reduced bythese windings, although they will, of course, have a small impedance.

As soon as the filaments become sufiiciently heated to emit enoughelectrons :to allow the lamps to start, current will flow in the chokecoils I! and I8, producing a counter-Voltage in the coils H, l2, l3, 14,which should be so proportioned as to balance out, as far as ossible,the voltage of the heater windings l, 8, 9, Hi, thus insuring that thecurrent to the filaments 3, 4, 5, 6, drops to a low value. Difference inphase may prevent complete balancing out of the current.

In order to make each lamp as independent as possible of the other, thewindings ll, I2 are preferably on the same core 21 as the choke H, andthe windings l3 and M on the same core 22 as the choke [8.

The transformer core 23 will ordinarily be separate from the choke core,although parts of their cores may be common as shown in Fig. 1, whichshows an arrangement suitable for the invention. In Fig. 1, thetransformer core 23 may have the transformer windings 7, 8, 9, It, ISand I6 wound thereon in the usual manner, the core only being shown forclarity. The magnetic circuit will be closed by arms 24, 25, 26 and 2?.The transformers may have as low leakage reactance as the constructionpermits.

The core 2| will have the coils H, M, 2 wound thereon and the core 22the coils it, Hi and E8. The cores 2! and 22 are closed to thetransformer core 24, 28 by the pieces 32, 23, 29, 39, 3! and 33 throughthe short air gaps 34, 35, 36, 31, 38 and 39. The core portions 24 and26 thus act as a common path for the transformer and a choke, but theremainder of the paths are separate. The metal piece, preferablynon-magnetic, helps to align the core and hold it in position. Thescrews 4i and 42 may pass through the piece 45, the core, and a similarpiece to 40 on the other side of the transformer, to be held by threadson a nut on said other side.

The flux from both the transformers and one of the choke coils flowsthrough arms 24 and 26 of the core shown in Fig. 1. Accordingly, if thefilament heating windings 1, 8, 9, are wound on these legs 24 and 26,they will supply voltage from the transformer flux to the filaments,prior to the starting of the lamp, and if the choke coil windings areconnected with their polarities such that the choke coil flux passesthrough legs 24 and 26 in a direction opposite to that of thetransformer flux, the total flux passing through the coil, will bereduced, with consequent reduction in the voltage supplied to theheater, once the lamp starts and current passes through the chokewindings. The reduction may be made sumcient to drop the filamentcurrent to a low value once the lamp starts, without requiring thecounter-voltage coils l I, l2, 13, Hi. However, placing coils on thelegs 24 and 25 makes the stacking of the core laminations a morecomplicated process. In addition, reduction of the heating current bythe countervoltage coils i more readily controlled and allows the coilsI, 8, l3 and [4 to be wound directly on leg 23 with the othertransformer windings.

When the heating current is to be reduced by the interaction of chokeand transformer flux, the two heating coils on each of" the legs 24 and25 are preferably arranged symmetrically, so that one coil is on theportion of the legs 24 and 26 between legs 23 and 25 and another on theportion between legs 23 and 21.

In order to reduce the maximum transformer voltage necessary to startthe lamp under all conditions, a film of moisture-dispersing material ispreferably used on the lamps. Without this coating on the lamps, a muchlarger starting voltage must be provided by the transformer, despite thefact that it will not be necessary to start the lamps under the majorityof conditions.

Although we have described a two lamp circuit for convenience, my deviceis obviously applicable to a single lamp circuit also, and the circuitof Fig. 1 will of course function if one lamp is omitted, for example,if one lamp reaches the end of 4 its life. The circuit can, of course,be used with as many lamps as desired.

What we claim is:

A lighting circuit comprising: a discharge lamp having two preheatablefilamentary electrodes each of said electrodes having two terminals; atransformer having a main secondary and having auxiliary secondaries forsupplying heating current to each of said filamentary electrodes, saidauxiliary secondaries being separate from each other and from said mainsecondary; a reactor having a main coil separate from each of said mainand auxiliary secondaries and connected in series with said mainsecondary and said discharge lamp, connections to the lamp being made toone terminal of each electrode; secondary windings on said reactor, eachof said secondary windings being separate from each other and from themain and auxiliary secondaries and from the main coil of the reactor,each of secondary windings on said reactor being connected inseries-opposing relationship with one of said auxiliary secondaries ofsaid transformer to produce a counter voltage to the voltage of theauxiliary secondary when current flows through the lamp and the maincoil of said reactor, one such auxiliary secondary of said transformerand one such secondary winding on said reactor being connected in serieswith the two terminals of one of the filamentary electrodes of saidlamp, the other of said auxiliary secondaries of the transformer and theother of said secondary windings of said reactor being connected inseries with th two terminals of the other of said filamentaryelectrodes, thereby reducing the current through said electrodes whencurrent flows through the lamp and the reactance coil.

BRUCE A. SAWYER.

LAURENCE BURNS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES General Elec. Review, Aug. 1944,pgs. 6-16.

